The present invention relates to a motor vehicle automatic transmission and, more particularly, to an improved automatic transmission having a hydrodynamic converter, clutches and brakes and having a Simpson gear set as a three-speed part and another planet gear set, a brake and a clutch which, together, form a fourth gear.
A transmission of this type is known from ATZ Automobiltechnische Zeitschrift 85 (1983)6, Page 393-398. The four-speed automatic transmission comprises a three-speed part, and the proven SIMPSON-brand gear set to which another planet gear set for the fourth speed was added which has a disk brake, a clutch and a one-way clutch.
The SIMPSON-brand gear set is a composite planetary transmission which comprises two simple planetary gears with a negative stationary gear ratio which are also called minus transmissions. In this case, one planetary transmission comprises a sun gear, a planet carrier having planetary wheels and a ring gear. Both minus transmissions are connected with one another by two coupling shafts. The first coupling shaft connects the sun gear of one planetary transmission with the sun gear of the second planetary transmission. The second coupling shaft connects the ring gear of the first planetary transmission with the planet carrier of the second planetary transmission. With the forward gears, the flux of force takes place from the outside to the ring gear of the second planetary transmission. The second coupling shaft serves as the output. The first speed of the SIMPSON-brand gear set is generated by the locking of the first planet carrier; the second speed is generated by the locking of the first coupling shaft. In the third speed, the flux of force acts simultaneously on the sun gear and the ring gear of the second planetary transmission, so that the Simpson gear set rotates as a block.
It is an object of the present invention to make the aforementioned type of transmission a five-speed or a six-speed transmission without any significant increase of the constructional expenditures and of the dimensions.
The foregoing object has been achieved by following the shifting arrangement of the SIMPSON-brand gear of the first and/or of the second gear with the shifting arrangement of the additional planet gear set used for an additional gear. Since the SIMPSON-brand shifting arrangement of a low gear speed is followed by the shifting arrangement of the additional planetary gear set used for another speed (for example, for the fourth speed) and thus a multiplication is achieved of the translational steps, an additional gear speed can be implemented without the requirement of having to constructionally change the entire transmission. Only corresponding clutches and/or brakes must be controlled for the shifting of the additional gear speed.